1. Field of the Invention
The present invention relates to power supply apparatuses, and in particular to technology for generating stable voltage that is not affected by noise.
2. Description of the Related Art
In various kinds of electronic devices, in order to supply a voltage higher or a voltage lower than a power supply voltage supplied from a battery or the like, to a load circuit, a step-up or a step-down switching power supply is used. For example, Patent Documents 1 and 2 disclose an insulating DC/DC converter as a switching power supply.
This type of switching power supply is configured to have a switching element for controlling current flowing in an inductor or a transformer. In this switching power supply, switching noise is generated from the switching element which turns ON and OFF at a high frequency during a stepping up or stepping down operation.    Patent Document 1: 2004-201474    Patent Document 2: 2005-73483
A switching power supply is provided with a control circuit which controls ON and OFF states of a switching element. This control circuit turns ON and OFF the switching element, based on a reference voltage outputted from a reference voltage source such as a bandgap reference circuit or the like, and stabilizes output voltage of the switching power supply.
Here, switching noise generated by the switching element has an impact on another circuit block connected via power supply wiring or the like. When the switching noise is inputted to the reference voltage source, since the noise is superimposed on the reference voltage, there is a risk that a stepping up or a stepping down operation will be hindered.